Method of making flexible veneer laminate



Patented Feb. 3, 1948 METHOD OF MAKING FLEXIBLE VENEER LAMINATE Armin Elmendorf, Winnetka, Ill., asslgnor to The Flexwood Company, a corporation of Illinois No Drawing. Application August 23, 1944,

Serial No. 550,867

1 Claim. (Cl. 154-132) 1 In my prior Patent No. 1,819,775 there is disclosed a composite sheet material, consisting of thin wood veneer bonded to a fiexible backing; the veneer being in .a ruptured-state so that it no longer constitutes a continuous membrane, but

consists of a mass of narrow strands or filaments which are not completely separated from each other. Although this material has been and is being widely used, the field of usefulness would be much greater except for certain conditions inherent in the material-that militate against a wider use.

The object of the present invention is to improve the aforesaid material so as not only to open wider fields of use therefor, but also to achieve more satisfactory results wherever it is used.

A further object is a novel method of making the composite flexible sheet material to make certain that the material will always have the new, desirable characteristics.

Flexwood is used mainly as a wall covering and, to be of maximum benefit to the public, the ordinary skilled paper hanger should be able to apply it. However, it has heretofore been found necessary to train specialists in the art of satisfactorily applying Flexwood to walls.-

Viewed in one of its aspects, the present invention may be said to have for its object to improve Flexwood in such a manner and to such an extent that the ordinary skilled paper hanger shall not only be able to apply it, but need not learn other skills or employ other tools than those with which he is already equipped.

One of the dlfliculties heretofore encountered in the use of Flexwood is the development of blisters after application to a wall. There are two main causes for this. If the adhesive is not uniformly distributed on the wall, so that there are scattered poorly bonded areas, the poor bonding usually will not be discovered until a day of high humidity comes. When that happens, the wood absorbs moisure and, in the areas of poor bonding, swells and separates the Flexwood from the wall; the result being blisters which do not subside completely upon drying of the wood but remain blistering from either of the aforesaid causes to a point where it is practically eliminated.

In its most highly developed form my invention contemplates also an improved finish on the face of the veneer. Heretofore the veneer has simply been sanded in the process of manufacture and, after having been applied to a wall. has been coated with lacquer or varnish; the ordinary paper hanger rarely doing a good finishing job paper, is that Flexwood is stiff in contrast to the fairly soft state in which wall paper is after being coated with paste. Therefore he cannot work Flexwood easily into corners, nor trim it by running a knife over the same along a base board, door or window frame or other shoulder against which the material is to be fitted. The first'thing to be considered in this connection is the thickness of the veneer. The thinner the veneer the more pliable it is; but if it is too thin little granules and surface defects present on the underlying wall will show through. From my researches I than .01 inch or more than .02 inch thick, al-' though withsome woods satisfactory results have been obtained with v a veneer thickness of one fortieth of an inch.

The likelihood of blisters'occurring can be reduced if the finished product on the wall will not expand materially upon becoming wet. Impregnating the veneer with synthetic resin partially accomplishes this purpose but leaves the veneer too brittle. In accordance with my invention I apply the veneer to the backing while it is wet and fully expanded, and 1. dry it and bond it under constraint: so that upon removing the composite sheet from the press the veneer is only one or two percent narrower than it was in its green state. When the press is opened and the constraint on the veneer is released, the veneer contracts elasticaliy to the extent of one or two percent of the width of the same in the green state. I have found that veneer bonded to a backing and dried in this manner expands only about one fourth as much as does veneer dried first and then bonded as heretofore. Hence the great reduction in the tendency to "produce blisters after application to a wall which I have noted with my improved product.

Heretofore it has always been the practice to bond the veneer to the backing while the veneer is dry, in order to avoid penetration of the glue through the veneer. I have discovered that even.

if a water soluble glue is spread over the backin coat.

' tact with the wax.

the wet thin veneer may be bonded satisfactorily if the glue coatis dry at the time without caus- -ing staining nor 'penetrationthrough the back- I ing if the adhesive be sparsely applied over a foundation coat that is appreciably less hygroscopic and less water soluble than the bonding The veneer need not contain all of its original I moisture at the time of bonding, but the moisture should not be appreciably below the fiber saturation: point which is of the order of 25% to 30%.

For the veneer bonding'coat I prefer, to use from five toten pounds of glue in liquid form to cover one thousand square feet of backing; the glue consisting of one part of dry animal glue to three parts of water. This is preferably applied over-a dry foundation coat that will block the absorbing of the adhesive by the backing; as, for example, a coat of urea adhesive properly cured. After the'bondingcoat'has dried, a sheet of the backing material and a sheet of wet veneer are assembled and placed in a hot press.

The backing should rest on a ventilating plate or screen i to providefor theesca'peof moisture during the pressingoperation. Where a screen is used it should not be "coarser than a 30x30 mesh and preferably a 50x50 mesh or finer. Between the a polished plate of metal that is not attacked by the chemicals which come out of the wood during the bonding operation. Stainless steel is satisiactory'for this purpose, In the press the assembly is subjected to a pressure adequate to produce at least 15% compression of: the face veneers in about minutes at a temperature of from 250 F. tov 300 F. The moisture in the veneer is driven through the backing and the screen and laterallyalongithe latter until it es capes along the edges of the sheets being dried and glued. The drying may take from one to two minutes, during which time the wood is plasticized and compressed. Following this the wood becomes case hardened, so that when the work leaves the press at the end.fi five or six minutes the veneer has a hardened,'polished surface.

Where a wax finish is desired, any conventional wax used for waxing floors or furniture may be applied to the polished face of the plate that is further, that this is possible even though the veneer is green and wet when it comes into con- The pressing time may be varied somewhat,

" but it should always be substantially greater than the time required to bond and dry the veneer. So'far as the temperature of the press is concerned, the lower the temperature the longer the time required to complete the operation; whereas, if the temperature be too high, discoloration of the wood may result. Generally, even though good gluing may be obtained at relatively low pressures, the resultant finish is dull and unsatisfactory if the final thickness of the veneer is not at lea'stliiyt less tha'n'its-air-dry thickness. If

the pressure he too high, so that the wood is compressedmore than about 45%, there may be discoloration of the wood, or the surface of the veneer may become rough, or the impression of v the wire screen may show through. While for 4 most veneers the range of permissible compression is from to 45% below the thickness of the veneer when allowed to air dry normally, some hard woods may acquire adequate sheen when the compression is slightly less than 15%, and for some very soft woods the compression .may be a little greater than 45% without introducing staining or other troubles.

Various kinds of backing materials may be employed. Good results have been obtained with thin, sized kraft paper and calendered chip paper about .009 inch thick.

Although I prefer to use animal glue to bond the veneer to the backing, almost any glue that does not stain the veneer can be used.

After the sheets leave the press they must be flexed to break up the veneer into narrow strands or filaments as described in my aforesaid patent. The strands in commercial Flex wood are not all of the same size, but they run about thirty two to the inch. This breaking up of the veneer results not only in flexing it but also in breaking into filaments any membrane finish, such as lacquer, which the veneer may veneer and the-upper platen of the press I place, v

have. If this were not done the moisture in the paste with which the sheet is subsequently attached to a wall would be trapped behind the veneer and could not escape to the atmosphere.

If the material is not waxed in the process of manufacture, a'finish such as lacquer or varnish may be applied after the material has been bonded to a wall. Such a finish i superior to that obtained when commercial sanded Flexwood sheets are finished on the job.

When pressed as described, the veneer face is smooth and polished while the paper back is embossed. The embossing facilitates bonding to the wall and improves the flexibility of the product.

It will thus be seen that while my improvement is a form of Flexwood, it is a great improvement on the older form: it has a case hardened, polished veneer face and an embossed back; the veneer has approximately the same width that it had in its'original green state, its capacity to expand has been largely nullified so that it can expand very little after application to a wall and blistering is thereby practically prevented; the veneer has been plasticized and flattened under heat and pressure; and the sheet as a whole becomes soft and limp when a wet adhesive is spread over the back preparatory to attaching it to a wall. Furthermore, it leave the press with a wax finish, if desired, so that the expense of subsequent finishing is avoided; It should further be noted that the characteristic softness and limpness of the product at the time of applying it to a well not only makes the application easier but permits it to be cut and trimmed in position.

It will also be seen that my method is a great improvement over the old method of making Flexwood because it plastlcizes, dries, bonds and polishes the veneer all in one operation; so that I have produced not only a product which to all intents and purposes solves completely the long standing problem of blistering, but also a new method by which the cost of manufacture and finishing the product is substantially lowered as is the cost of applying it to a wall.

I claim:

The method of making a flexible, composite, wood-faced sheet of material applicable as a wall finish, and having a polished. hardened,

compressed outer wood surface, which comprises simultaneously bonding a single sheet of thin wood veneer having a moisture content approximating or exceeding the fibre saturation point, to a flexible backing, and drying the veneer and hardening and compressing the veneer, by subjecting the assembly to heat and pressure adequate to compress the veneer from 15% to 45% less than its normal air-dry thickness, while maintaining the exposed face of the wood veneer in contact with a smooth, polished plate effective to prevent the escape of steam through the face of the veneer, and employing the moisture of the veneer to plasticize the face of the veneer and to impart a hardness substantially greater than the hardness of the kiln dried wood.

ARMIN ELMENDORF.

REFERENCES CITED The following references are of record in the 20 flle of this patent:

Number Number OTHER REFERENCES 'I Zrans Am. Soc. Mech. Eng., vol. so (1938), pp. 69- o. 

